If you don't mind listening to two voices at once, Navigon's MobileNavigator will continue giving turn-by-turn directions over music and incoming phone calls.Photo by Navigon/YouTube

Last week, TomTom announced its intentions to support Apple iOS 4's new multitasking function with its turn-by-turn navigation app. This week, we find Navigon, manufacturer of GPS devices and provider of the Navigon MobileNavigator app for iPhone, joining the chorus of developers singing praises of the iPhone's new ability to walk and chew bubble gum at the same time. However, Navigon's announcement comes with a video demonstration of the feature in action.

In the clip below, our guide Ben starts by jumping between the MobileNavigator app and Safari on an iPhone 3GS. Next, he moves on to initiating turn-by-turn directions with the navigation app. A few turns into the trip, he receives a phone call from a colleague name Sanja, which he proceeds to answer. During his short phone call, we are able to hear MobileNavigator's faint spoken turn instructions going on in the background.

It's not made clear whether or not poor Sanja would be forced to listen to the spoken directions or not (we certainly hope that's not the case). Also, the video doesn't demonstrate the app's ability to jump back to the map view while a call is in progress, a feature we know the current iPhone firmware supports. However, with iOS 4 just around the corner and an update to the Navigon MobileNavigator app soon to follow, we'll have those blanks filled in soon enough.